Knob locks are foam gaskets that will hold your settings in place when your pedal is being knocked about. A rubber sink washer will work, but those are hard to find in black, let alone purple to match your Black Spiral LED. Spiral Electric FX Pedal Knob Locks are designed to fit 1mm larger than the knobs on the pedal, and include a triple-thick version for the bias knob.
Installation is Easy
1 - Release the screw and remove the knob.
2 - Place the Knob Lock.
3 - Replace the knob and push down for a tight hold.
4 - While holding the knob down, re-tighten the screw.
BUY: Knob Locks Pack